CN103078520A - Frequency converter device and over-current protection method thereof - Google Patents
Frequency converter device and over-current protection method thereof Download PDFInfo
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- CN103078520A CN103078520A CN2012104062718A CN201210406271A CN103078520A CN 103078520 A CN103078520 A CN 103078520A CN 2012104062718 A CN2012104062718 A CN 2012104062718A CN 201210406271 A CN201210406271 A CN 201210406271A CN 103078520 A CN103078520 A CN 103078520A
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Abstract
The invention discloses a frequency converter device and an over-current protection method thereof. The frequency converter device is provided with a frequency conversion part, a phase current detection part and an over-current judgment part. All bridge arms of the frequency conversion part are respectively connected with all phase lines. As far as all the bridge arms, the bridge arms are respectively divided into an upper bridge arm and a lower bridge arm by connection nodes respectively connected with the phase lines; each upper bridge arm and each lower bridge arm are respectively provided with a switching element for switching on/off the corresponding bridge arm; the phase current detection part comprises a plurality of bridge arm resistors and a current detection part; the bridge arm resistors are respectively arranged on respective lower bridge arms of all the bridge arms; the current detection part is used for detecting respective voltages of both ends of each bridge arm resistor and outputting all phase current; the over-current judgment part comprises a prospective current operation part and a comparing part; the prospective current operation part is used for calculating a prospective current value generated in the later switching period by taking the phase current of the current switching period received from the phase current detection part as the reference; the comparing part is used for comparing the prospective current value with an over-current reference value; and if the prospective current value is greater than the over-current reference value, an over-current protection circuit is enabled to actuate.
Description
Technical field
The present invention relates to a kind of frequency-converter device; relate in particular to a kind of the have frequency-converter device of excess current protective function and the overcurrent protection method of this frequency-converter device; this excess current protective function refers to; the state of the overcurrent that judgement occurs in frequency-converter device, and execution is used for the function of the action of this overcurrent of inhibition.
Background technology
Frequency-converter device is the power inverter of the three-phase alternating current of a kind of electric power with assigned frequency impulse form of being converted to optional frequency.Frequency-converter device is because having the advantages such as energy-conservation and easy control output, so through being usually used in driving the motor that is widely used in the electric products such as washing machine, refrigerator, air-conditioning.
Usually, correctly control motor in order to utilize above-mentioned frequency-converter device, adopt following method: detect and put on the phase current of motor, and according to the phase current that detects, control the electric current that puts on motor by pulse width modulation (PWM) mode.
When detecting the phase current of motor, usually adopt Hall current sensor (Hall CT).The waveform of each the phase phase current that detects by Hall current sensor at this moment, is shown in the (a) and (b) of Fig. 9, (c).In Fig. 9, be the current waveform that utilizes the W phase that Hall current sensor detects (a), (b) be the current waveform of V phase, (c) be the current waveform of U phase.Shown in the (a) and (b) of Fig. 9, (c), although the waveform of the phase current of each phase that detects by Hall current sensor comprises a small amount of high-frequency harmonic, roughly be sinusoidal wave form.
With regard to general universal frequency converter device, all has the circuit overcurrent protection for the protection of frequency-converter device.Fig. 1 shows the decision circuitry in the circuit overcurrent protection of existing frequency-converter device.In the decision circuitry of Fig. 1, amplify by the phase current of operational amplifier to the sine wave of each phase of being detected by above-mentioned Hall current sensor, and calculate the phase current sum of each phase after the amplification, this phase current sum that then will calculate compares with the reference current value that predetermines, and judges whether overcurrent has occured in frequency-converter device.Under the phase current sum is situation more than the reference current value, reduce the output frequency of frequency-converter device or disconnect all switch elements, flow and initiating failure in frequency-converter device to avoid excessive electric current, thus the protection frequency-converter device.
But, with regard to cheapness, low capacity frequency-converter device, do not adopt the aforesaid method that detects phase current by Hall current sensor, and adopt following phase current detection method: the bottom brachium pontis at each brachium pontis (Leg) of this frequency-converter device arranges arm resistance (shunt resistance), utilizes the both end voltage of this arm resistance to detect phase current.This is because it is not only cheap to utilize arm resistance to detect the method for phase current, and the parts of the method take up space also little much than Hall current sensor, so has lot of advantages aspect mechanism design.
Utilize the waveform of the electric current that flows through each arm resistance R1, R2, R3 that arm resistance detects shown in (d), (e) of Fig. 9, (f).(d) of Fig. 9 is the waveform of the electric current among the arm resistance R3 that flows through on the bottom brachium pontis that is arranged on the brachium pontis that is connected with the W phase phase line of frequency-converter device, (e) being the waveform of the electric current among the arm resistance R2 that flows through on the bottom brachium pontis that is arranged on the brachium pontis that is connected with the V phase phase line of frequency-converter device, (f) is the waveform of the electric current among the arm resistance R1 that flows through on the bottom brachium pontis that is arranged on the brachium pontis that is connected with the U phase phase line of frequency-converter device.Shown in (d), (e) of Fig. 9, (f), the electric current that flows through each arm resistance R1, R2, R3 has interrupted waveform, therefore according to the phase angle of output waveform, can be difficult to detect the interval of electric current, and, the form of the phase current of each phase that calculates according to such electric current that flows through each arm resistance also has interrupted waveform, also can not have sinusoidal wave form as the phase current that detects by Hall current sensor.
About utilizing arm resistance to detect method and the interrupted concrete reason of waveform of such electric current, the later on again narration of the phase current of each phase.
The degree that such current waveform is interrupted can become more serious along with the increase (along with pulse duration becomes large) of the operating frequency in the V/F running.If operating frequency becomes more than the assigned frequency (being generally rated frequency), then under extreme situation, also might can't detect electric current by arm resistance.Under such operating condition, the two ends of arm resistance do not produce voltage, therefore can't detect phase current.
Under these circumstances, certainly can calculate by the electric current that the arm resistance on other brachium pontis is flow through in detection the phase current of this phase.But, calculate electric current by software, then need the regular hour, this can make as to operate time sensitivity the circuit overcurrent protection of protective circuit can't give full play to defencive function.Its result, the problem that can cause the stability of whole system to reduce.
That is, if the phase current that will detect by the phase current detection method that utilizes arm resistance is directed into the decision circuitry of existing circuit overcurrent protection as shown in Figure 1, then the actual time that can detect electric current can be restricted according to the polarity of electric current.Therefore, constant although the grade that overcurrent suppresses is not subjected to the impact of polarity of electric current, when the detection error because of electric current was judged as overcurrent, the asymmetric situation of electric current can occur.
Summary of the invention
The present invention excessively rises so that the problem of frequency-converter device fault proposes because such electric current is asymmetric in order to solve output current; its purpose is to provide frequency-converter device with excess current protective function and the overcurrent protection method of this frequency-converter device; this excess current protective function refers to; in current switch periods; detect electric current by hardware; detect output over-voltage according to the Current rise value till the switch periods of current detecting result after calculating and predicting; thereby in the situation of output voltage not being out of shape, also can produce the excess current protective function of desired output voltage.
To achieve these goals, the frequency-converter device of a mode of the present invention, by the pulse width modulation that utilizes the pwm signal pattern industrial power is converted to the alternating voltage of optional frequency and puts on load, this pwm signal pattern is based on carrier signal and input signal generates, it is characterized in that
Have:
Frequency conversion section, each brachium pontis of this frequency conversion section is connected with each phase line of above-mentioned load respectively, with regard to the arbitrary brachium pontis in above-mentioned each brachium pontis, the connected node that this brachium pontis is connected by the phase line of this brachium pontis and above-mentioned load is divided into top brachium pontis and bottom brachium pontis, be respectively equipped with for the switch element that comes this brachium pontis of on/off according to the said PWM signal pattern at above-mentioned top brachium pontis and bottom brachium pontis
The phase current test section, comprise a plurality of arm resistances and current detecting part, above-mentioned a plurality of arm resistance is separately positioned on the bottom brachium pontis of each brachium pontis of above-mentioned frequency conversion section, and above-mentioned current detecting part is for detection of the voltage at the two ends of above-mentioned each arm resistance and export the phase current of each phase
Over-current judging section, comprise prospective current operational part and comparing section, the phase current of the current switch periods that above-mentioned prospective current operational part will be in based on the switch motion of said PWM signal pattern receives from above-mentioned phase current test section is as benchmark, prediction and calculation after switch periods in the prospective current value that may occur, above-mentioned comparing section compares prospective current value and the predefined overcurrent fiducial value that calculates;
Be above-mentioned overcurrent fiducial value when above in above-mentioned prospective current value, make the circuit overcurrent protection action.
With regard to above-mentioned frequency-converter device, be preferably, the maximum current upstroke slope that the utilization of above-mentioned prospective current operational part predetermines, according to the phase current values of current switch periods, prior forecast calculates the phase current values of next switch periods adjacent with current switch periods as above-mentioned prospective current value.
With regard to above-mentioned frequency-converter device, above-mentioned load is alternating current motor,
Be made as Vs at the voltage that will put on above-mentioned motor, the inductance value of above-mentioned motor is made as Ls, when above-mentioned maximum current upstroke slope is made as slope, can utilize relational expression slope=Vs/Ls to decide above-mentioned maximum current upstroke slope.
With regard to above-mentioned frequency-converter device, can utilize the automatic regulating function of above-mentioned frequency-converter device to come the inductance value of the above-mentioned motor of automatic acquisition.
With regard to above-mentioned frequency-converter device, determine that above-mentioned maximum current upstroke slope can adopt following method: the upstroke slope of the output current of actual measurement frequency-converter device and make up database in the real-world operation process, and continue the maximum upstroke slope in the upstroke slope of these output currents is upgraded, determine thus above-mentioned maximum current upstroke slope.
With regard to above-mentioned frequency-converter device, be made as iu1 at the phase current with above-mentioned current switch periods, the phase current of above-mentioned next switch periods is made as iu2, the cycle of above-mentioned carrier signal is made as Ts, when above-mentioned maximum current upstroke slope is made as slope, can utilize relational expression iu2=slope * Ts+iu1 to calculate above-mentioned prospective current value.
With regard to above-mentioned frequency-converter device, be preferably 2～3 times of the rated current that above-mentioned overcurrent fiducial value is above-mentioned frequency-converter device.
With regard to above-mentioned frequency-converter device, be preferably, above-mentioned current detecting part comprises:
Current detector, the voltage at the two ends of above-mentioned each arm resistance of detection, Flow is crossed the electric current of above-mentioned each arm resistance thus;
The phase current operational part according to the current value that above-mentioned current detector calculates, calculates and exports the phase current of each phase.
With regard to above-mentioned frequency-converter device, be preferably, above-mentioned current detector is integrated operational amplifier.
With regard to above-mentioned frequency-converter device, be preferably, above-mentioned arm resistance is noninductive resistance.
With regard to above-mentioned frequency-converter device, also can be according to the phase current values of the waveform characteristic value of above-mentioned input signal, above-mentioned current switch periods and the phase information of this phase current values, calculate the maximum of waveform of this phase current of particular phases in the cycle as above-mentioned prospective current value, the above-mentioned particular phases cycle refers to that this phase current values is residing phase cycling in the phase current waveform of this phase.
In addition; in order to realize above-mentioned purpose; the overcurrent protection method of the frequency-converter device of another way of the present invention; by the pulse width modulation that utilizes the pwm signal pattern industrial power is converted to the alternating voltage with optional frequency and puts on load; this pwm signal pattern is based on carrier signal and input signal generates; it is characterized in that
Above-mentioned frequency-converter device has:
Frequency conversion section, each brachium pontis of this frequency conversion section is connected with each phase line of above-mentioned load respectively, with regard to the arbitrary brachium pontis in above-mentioned each brachium pontis, the connected node that this brachium pontis is connected by the phase line of this brachium pontis and above-mentioned load is divided into top brachium pontis and bottom brachium pontis, be respectively equipped with for the switch element that comes this brachium pontis of on/off according to the said PWM signal pattern at above-mentioned top brachium pontis and bottom brachium pontis
A plurality of arm resistances are separately positioned on the bottom brachium pontis of each brachium pontis of above-mentioned frequency conversion section;
The overcurrent protection method of above-mentioned frequency-converter device comprises:
Determine the step of maximum current upstroke slope,
Detect the voltage at the two ends of above-mentioned each arm resistance, and calculate the phase current of each phase of current switch periods and the step of carrying out the A/D conversion according to detected voltage,
On the basis of the phase current values of the current switch periods that A/D changed and above-mentioned maximum current upstroke slope, the step of the expection phase current values of next switch periods that prediction and calculation is adjacent with current switch periods,
With the expection phase current values of next switch periods of calculating and the step that predefined overcurrent fiducial value compares;
Be above-mentioned overcurrent fiducial value when above in above-mentioned prospective current value, make the circuit overcurrent protection action.
If employing the present invention, the Current rise value till the switch periods after then calculating and predicting detects output over-voltage, thereby in the situation of output voltage not being out of shape, also can produce desired output voltage.Thus, the situation of overcurrent will occur in prior forecast, and makes the protective circuit action, thereby can realize more stable protection action.
Description of drawings
Fig. 1 is the decision circuitry in the circuit overcurrent protection of existing frequency-converter device.
Fig. 2 is the structure chart of the frequency-converter device with excess current protective function of one embodiment of the invention.
Fig. 3 utilizes the phase current test section of the frequency-converter device of one embodiment of the invention to detect the figure of method of the phase current of each phase for explanation.
Fig. 4 is the space vector of voltage figure when using the frequency-converter device of one embodiment of the invention.
Fig. 5 is the figure for the interrupted reason of the waveform of the output current phase of the phase current test section of the frequency-converter device of explanation one embodiment of the invention.
Fig. 6 is the figure for the interrupted reason of the waveform of the output current phase of the phase current test section of the frequency-converter device of explanation one embodiment of the invention.
Fig. 7 is the figure that schematically shows the relation between the maximum current upstroke slope of pwm signal pattern, input signal, carrier signal and phase current of common frequency-converter device.
Fig. 8 is the flow chart of overcurrent protection method of the frequency-converter device of one embodiment of the invention.
The figure that Fig. 9 shows the waveform of the phase current that utilizes each phase that Hall current sensor detects and utilizes the waveform of the electric current that flows through each arm resistance that arm resistance detects, wherein, (a) be the current waveform that utilizes the W phase that Hall current sensor detects, (b) be the current waveform of V phase, (c) be the current waveform of U phase, (d) be the waveform that utilizes the electric current that flows through the arm resistance R3 on the bottom brachium pontis that is arranged on the brachium pontis that is connected with the W phase phase line of frequency-converter device that arm resistance detects, (e) being the waveform that flows through the electric current of the arm resistance R2 on the bottom brachium pontis that is arranged on the brachium pontis that is connected with V phase phase line, (f) is the waveform that flows through the electric current of the arm resistance R1 on the bottom brachium pontis that is arranged on the brachium pontis that is connected with U phase phase line.
The explanation of Reference numeral
1 ... industrial power
2 ... rectification part
21 ... diode sequence 22 ... smmothing capacitor 23 ... charging circuit 24 ... braking circuit
3 ... frequency conversion section
VT1～VT6 ... switch element
4 ... efferent
5 ... modulation portion
6 ... control part
7 ... the phase current test section
R1, R2, R3 ... arm resistance 71 ... current detecting part
71A, 71B, 71C ... current detector 711 ... the phase current operational part
8 ... over-current judging section
81 ... phase current A/D converter section 82 ... prospective current operational part 83 ... comparing section
Specific embodiment
Below, with reference to accompanying drawing, specific embodiments of the invention are elaborated.
Fig. 2 is the structure chart of the frequency-converter device with excess current protective function of one embodiment of the invention.
As shown in Figure 2, the frequency-converter device with excess current protective function of one embodiment of the invention, on the basis of common converter circuit, also comprise phase current test section 7 and be arranged at phase current test section 7 and control part 6 between over-current judging section 8.Wherein, common converter circuit comprises: rectification part 2, industrial power 1 is carried out the rectification line output of going forward side by side; Frequency conversion section 3 will convert the three-phase alternating voltage (U, V, W) of the pulse mode with optional frequency to and supply with efferent 4 from the direct voltage of above-mentioned rectification part 2 outputs by pulse width modulation (PWM), thus the drive motor even load; Modulation portion 5 receives that carrier wave (switch) the signal Uc input and input signal Ur generate the pwm signal pattern and to 3 outputs of above-mentioned frequency conversion section, thereby drives above-mentioned frequency conversion section 3; Control part 6 by inputing to modulation portion 5 for carrier signal Uc and input signal Ur that the pwm signal pattern occurs, is controlled the action of frequency conversion section 3.
Above-mentioned rectification part 2 can comprise: diode sequence 21, the alternating current (R, S, T) of industrial power 1 is carried out rectification; Smmothing capacitor 22 carries out smoothing processing to the voltage from 21 outputs of diode sequence; Charging circuit 23 prevents from producing excessive inrush current when smmothing capacitor 22 is carried out initial charge; When braking circuit 24, motor are brought back to life (produce power) in operation process, prevent that the voltage of smmothing capacitor 22 from excessively rising.
Above-mentioned frequency conversion section 3 is common switching circuit, each brachium pontis of above-mentioned frequency conversion section 3 is connected with each phase line of load (for example being motor) respectively, arbitrary brachium pontis in each brachium pontis like this, the connected node that this brachium pontis is connected with the phase line of load by this brachium pontis is divided into top brachium pontis and bottom brachium pontis, be respectively equipped with for the switch element that comes this brachium pontis of on/off according to the said PWM signal pattern at above-mentioned top brachium pontis and bottom brachium pontis, the above-mentioned frequency conversion section 3 PWM switch element sequence by being consisted of by so a plurality of switch elements, direct voltage is converted to three-phase alternating voltage (U, V, W), and with this three-phase alternating voltage supply with the motor even load.
Usually, with be located in two switch elements on each brachium pontis some connections then the mode of another disconnection frequency conversion section 3 is controlled, therefore, when all on off states of expression frequency conversion section 3, usually utilize switch element VT1, the VT3 on the brachium pontis of top, the state of VT5 to represent.
Above-mentioned control part 6 is controlled the action of frequency conversion section 3 by existing pulse width modulation (PWM) mode.In order to control the speed of motor, with the expectation input signal Ur(of each phase usually the phase difference of the input signal of each phase be 120 degree) and the expectation carrier signal Uc(that produces of clock generator (not shown) by switching frequency each can share between mutually) input to modulation portion 5, wherein, this expectation carrier signal Uc refers to, the reference waveform that the maximum level of the input signal Ur of each phase of peakedness ratio is larger (triangular wave or sawtooth waveforms).
In modulation portion 5, come this carrier signal Uc is compared with each input signal Ur mutually by comparator, forming the PWM modulation is the pwm signal pattern with waveform.
Fig. 7 is the figure that schematically shows the relation between the maximum current upstroke slope of pwm signal pattern, input signal, carrier signal and phase current of common frequency-converter device.
Their resulting PWM modulation of carrier signal Uc and input signal Ur and comparison with impulse waveform as shown in Figure 7.With regard to any of upper switches element VT1, VT3, VT5, at the input signal of the phase of answering with this upper switches elements relative during greater than carrier signal, the pwm signal pattern becomes " H ", less than carrier signal the time, the pwm signal pattern becomes " L " (with reference to the pwm signal pattern of the VT1 among Fig. 7).Its result, the pwm signal pattern forms the impulse waveform that the on/off ratio is directly proportional with input signal.
Above-mentioned phase current test section 7 comprises: 3 arm resistance R1, R2, R3 are separately positioned on the bottom brachium pontis of each brachium pontis of frequency conversion section 3; Current detecting part 71 detects the voltage at each arm resistance R1, R2, R3 two ends, and exports the phase current of each phase according to the voltage detecting result.
Fig. 3 utilizes the phase current test section of one embodiment of the invention to detect the figure of method of the phase current of each phase for explanation, wherein simply shows each switch element VT1～VT6, and is connected with three-phase alternating-current motor at efferent 4.
Below, with reference to Fig. 3, above-mentioned phase current test section 7 and the method that detects the phase current of each phase by this phase current test section 7 are elaborated.
Above-mentioned current detecting part 71 comprises: current detector 71A, 71B, 71C, detection is separately positioned on the voltage at the two ends of 3 arm resistance R1, R2 on the bottom brachium pontis of each brachium pontis of frequency conversion section 3, R3, and Flow is crossed the electric current of each arm resistance R1, R2, R3 thus; Phase current operational part 711 according to the current value that current detector 71A, 71B, 71C calculate, calculates and exports phase current iu, iv, the iw of each phase. Current detector 71A, 71B, 71C can use integrated operational amplifier (integratedoperational amplifier).
On the other hand, can be illustrated by following formula to each arm resistance R1, R2 of phase current test section 7, the voltage that the two ends of R3 apply.
u=i×R+l×di/dt
Wherein, u is the voltage at arm resistance two ends, and i is the electric current that flows through arm resistance, and l is the stray inductance of arm resistance, and di/dt is the differential value of electric current for the time.
Can find out from above-mentioned formula, in order to ensure the correctness of Current calculation, preferably should eliminate as much as possible the impact that the stray inductance of arm resistance is brought to voltage.Therefore, preferably adopt noninductive resistance.
And as mentioned above, the frequency-converter device of one embodiment of the invention utilizes pulse width modulation (PWM) to control the action of 6 switch elements.And, to be located at the some connections mode of another disconnection then in two switch elements on each brachium pontis, the switch element of frequency conversion section 3 is controlled, usually, be shown as 1 or 0 by the state with upper switches element VT1, VT3, VT5, represent the open/close state of all switch elements.At this moment, 1 expression switch connection and the state of switching on, the state that 0 expression switch disconnects.
In situation about controlling in such pulse width modulation (PWM) mode, the switch element of frequency conversion section 3 is in a certain state in 6 kinds of on off states corresponding with the combination of the on/off of each switch element VT1～VT6.Modulation portion 5 is controlled each switch element by corresponding with above-mentioned 6 on off states respectively pwm signal pattern occurs.
Fig. 4 is the space vector of voltage figure when using the frequency-converter device of one embodiment of the invention, and " 100 "～" 101 " that mark on hexagonal each summit correspond respectively to the on/off state of each upper switches element VT1, VT3, VT5.And, the on/off state of lower switches element VT4, VT6, VT2 respectively with the on/off opposite states of upper switches element VT1, VT3, VT5.
Situation when Fig. 3 shows space vector of voltage and is arranged in the first sector of space vector of voltage figure shown in Figure 4.
With reference to Fig. 3 and Fig. 4, the phase current values that will flow through each phase line of three-phase alternating-current motor is made as respectively iu, iv, iw, to be made as iu_ad, iv_ad, iw_ad from the current value of each current detector 71A, 71B, 71C output, to be made as to the sense of current that three-phase alternating-current motor flows into "+" direction, to be made as from the sense of current that three-phase alternating-current motor flows out "-" direction, so, as shown in table 1 below corresponding to the current value that flows through each arm resistance under the on off state of each sector and the relational expression between each phase current.
Therefore in addition, in the situation that three-phase alternating-current motor does not break down, the load on each phase line symmetrical (that is, each phase load value is identical) under on off state is 110,101 and 011 situation, also can calculate the phase current of each phase.For example, be in 110 the situation on off state, since symmetrical in each load of going up mutually, relational expression iu=iv=iw/2=iw_ad/2 therefore set up.Similarly, be in 101,011 the situation, also can draw relational expression as shown in table 1 below on off state.
Table 1
Namely, in above-mentioned phase current test section, the voltage that current detector 71A, 71B, 71C detect the two ends of each arm resistance R1, R2, R3 calculates the current value that flows through each arm resistance R1, R2, R3, phase current operational part 711 utilizes each relational expression shown in the above-mentioned table 1, calculates and export the instant value of the phase current of each phase according to the current value from current detector 71A, 71B, 71C output.
But as shown in Figure 9, the electric current that flows through each arm resistance has interrupted waveform, and at this moment, the output current of phase current test section 7 also has interrupted waveform.
Fig. 5 is the figure for the interrupted reason of the waveform of the output current phase of the phase current test section of the frequency-converter device of explanation one embodiment of the invention.
Fig. 6 is the figure for the interrupted reason of the waveform of the output current phase of the phase current test section of the frequency-converter device of explanation one embodiment of the invention.
Below, with reference to Fig. 5 and Fig. 6, the interrupted concrete reason of waveform of the output current phase of the phase current test section of the frequency-converter device of one embodiment of the invention is described.
The interrupted concrete reason of the waveform of the output current phase of phase current test section 7 is, as shown in Figure 5, if upper switches element VT1 keeps on-state, then as mentioned above, the lower switches element VT4 corresponding with upper switches element VT1 is in off-state, so electric current does not flow through arm resistance R1, the voltage at the two ends of arm resistance R1 becomes 0, therefore can't detect voltage.As shown in Figure 6, only be switched on and electric current when flowing through arm resistance R1 at lower switches element VT4, just can detect the electric current that flows through arm resistance R1.Because such reason, the electric current that flows through arm resistance that current detector 71A detects has interrupted form.
Such as Fig. 7 diagram, along with the variation that the phase place of input signal Ur is namely exported the phase place of phase voltage, can there be the interval elongated zone of conducting of upper switches element VT1.If the conducting interval of upper switches element VT1 is elongated, then the ON time of lower switches element VT4 shortens, so the time that electric current flows through arm resistance shortens.At this moment, as shown in Figure 9, the waveform that flows through the electric current of each arm resistance is the form of discontinuous sine wave.Therefore, the form of the phase current of each phase that calculates according to such electric current that flows through each arm resistance also has interrupted waveform, and has sinusoidal wave form unlike the phase current that is detected by Hall current sensor.
The degree that such current waveform is interrupted can become more serious along with the increase (along with pulse duration becomes large) of the operating frequency in the V/F running.In other words, if the raising operating frequency, then the turn-on time of upper switches element VT1 is elongated, relative therewith, can shorten the turn-on time of lower switches element VT4, so the interrupted degree of the waveform of the phase current that phase current test section 7 is exported can become more obvious.
If operating frequency is more than the assigned frequency (being generally rated frequency), then in extreme situation, may there be the interval of lower switches element VT4 connection, thereby can't detects the electric current that flows through arm resistance.Under these circumstances, do not produce voltage at the two ends of arm resistance, therefore can't detect phase current.
Under these circumstances, certainly can calculate by the electric current that the arm resistance on other brachium pontis is flow through in detection the phase current of this phase of current switch periods.But; to calculate electric current by software; then need the regular hour, thus if the phase current of each phase that will obtain like this is directed in the existing circuit overcurrent protection, then as to operate time sensitivity the circuit overcurrent protection of protective circuit can't give full play to defencive function.
Therefore, such as Fig. 2 diagram, the over-current judging section 8 of present embodiment comprises: phase current A/D converter section 81, carry out the A/D conversion to the phase current values that receives from phase current test section 7; Prospective current operational part 82 will be based on the phase current of the current switch periods of the switch motion of pwm signal pattern as benchmark, prediction and calculation after switch periods in the prospective current value that may occur; Comparing section 83, prospective current value and predefined overcurrent fiducial value that prospective current operational part 82 is calculated compare, and export the result of this comparison to control part 6.
When the prospective current value is that the overcurrent fiducial value is when above; control part 6 is judged as frequency-converter device the output overcurrent has occured; reduce the output frequency of frequency-converter device or disconnect all switch elements; avoiding excessive electric current in frequency-converter device, to flow and initiating failure, thus the protection frequency-converter device.
When selected above-mentioned overcurrent fiducial value, calculate the overcurrent fiducial value according to the capacity of frequency-converter device take the rated current of frequency-converter device as benchmark.Usually, with 2～3 times value of the rated current of frequency-converter device as the overcurrent fiducial value.But, this overcurrent fiducial value is not limited to aforesaid benchmark, and according to the difference of frequency-converter device producer and difference, and so long as in the overload running (usually, the value that frequency-converter device is destroyed 150%, one minute kind of output-current rating) gets final product.Selected overcurrent fiducial value inputs to comparing section 83 by not shown input part.
The method of prospective current operational part 82 prediction and calculation prospective current values is as follows.
Fig. 7 shows turn-on time of lower switches element VT4 and situation about shortening and electric current form of under these circumstances phase current iu elongated along with the turn-on time of upper switches element VT1.With reference to Fig. 7, prospective current operational part 82 is according to the phase current values of the first switch periods of being changed by phase current A/D converter section 81A/D, next switch periods that always calculated in advance is adjacent with the first switch periods is the Current rise value based on maximum current upstroke slope slope in second switch cycle, and calculates the phase current values in second switch cycle according to this Current rise value.
The calculating of maximum current upstroke slope can be adopted following several method.
For example, so long as those skilled in the art are clear, if the inductance value Ls of known electric motor and the voltage Vs that puts on motor then can calculate maximum current upstroke slope slope between the adjacent switch periods by following formula.
slope=Δiu/Ts=（iu2-iu1）/Ts=Vs/Ls
In following formula, Δ iu is illustrated in the Current rise value of phase current (putting on the electric current of the motor) iu between the adjacent switch periods, the phase current iu2 that namely represents the second switch cycle with as the difference between the phase current iu1 of the first switch periods of the switch periods before adjacent with this second switch cycle, Ts represents that the time interval between the adjacent switch periods is the cycle of carrier signal Uc, Vs represents to put on the voltage of motor, and Ls represents the inductance value of motor.
At following formula as can be known, when the automatic adjustment that utilizes frequency-converter device (Auto tuning) function is come the inductance value Ls of automatic acquisition motor, and during voltage (output voltage of the frequency-converter device) Vs that utilizes not shown voltage measuring apparatus to measure to put on motor, can calculate maximum current upstroke slope slope, and according to this maximum current upstroke slope slope that calculates and the phase current iu1 of the first switch periods, can calculate the phase current iu2(=slope in second switch cycle * Ts+iu1).
Except the computational methods of aforesaid maximum current upstroke slope, can also decide by such method the maximum current upstroke slope: utilize the measured value in the real-world operation process, make up the database of the gradient of the output current of the output voltage of frequency-converter device and frequency-converter device, and continue the maximum upstroke slope in these gradients is upgraded (update), determine thus the maximum current upstroke slope.
Below, the overcurrent protection method of the frequency-converter device of one embodiment of the invention is described.
Fig. 8 is the flow chart of overcurrent protection method of the frequency-converter device of one embodiment of the invention.
With reference to Fig. 8, at first, the prospective current operational part 82 of over-current judging section 8 decides maximum current upstroke slope slope(step (following referred to as S) 101 by above-mentioned method).
81 pairs of the phase current A/D converter sections of over-current judging section 8 carry out A/D conversion (S102) from the phase current iu1 of the current switch periods that phase current test section 7 receives.
The prospective current operational part 82 of over-current judging section 8 is according to the cycle T s of the phase current iu1 of the maximum current upstroke slope slope that obtains at S101, A/D changed in S102 current switch periods and known carrier signal Uc, calculates the expection phase current values iu2(=slope of next switch periods * Ts+iu1).That is, over-current judging section 8 on the basis of the phase current values of the current switch periods that A/D changed and maximum current upstroke slope slope, the expection phase current values (S103) of next switch periods that prediction and calculation is adjacent with current switch periods.
The expection phase current values of next switch periods that comparing section 83 will calculate at S103 with compare (S104) by the overcurrent fiducial value by the regulation that determines as described above.
If the expection phase current values of next switch periods is the overcurrent fiducial value of regulation above (be "Yes" at S104); then control part 6 is judged as frequency-converter device the output overcurrent has occured; make the circuit overcurrent protection action; reduce the output frequency of frequency-converter device or disconnect all switch elements; avoiding excessive electric current in frequency-converter device, to flow and initiating failure, thus protection frequency-converter device (S105).
If the expection phase current values of next switch periods is less than the overcurrent fiducial value (be "No" at S104) of regulation, then the pwm signal pattern by occuring from carrying out normal load operation (S106) in control part 6.
Above with reference to accompanying drawing, be illustrated for frequency-converter device and the overcurrent protection method with excess current protective function of the present invention, but these contents are most preferred embodiments of the present invention, can not be considered as limitation of the invention.
For example; for example understand in the above-described embodiments the three phase converter device; but of the present invention have the frequency-converter device of excess current protective function and an overcurrent protection method of this frequency-converter device; also can be applicable to the frequency-converter device of the above phase of three-phase; at this moment; as long as respectively with each brachium pontis that the phase line of each phase of frequency-converter device is connected on, with each brachium pontis of the frequency conversion section of the frequency-converter device of above-described embodiment switch element, arm resistance and integrated operational amplifier are set similarly and get final product.
Also have, illustrated that in the above-described embodiments it is the mode of the phase current in second switch cycle that phase current according to the first switch periods comes prediction and calculation next switch periods adjacent with this first switch periods, but the present invention is not limited thereto.For example, although because from the waveform of the phase current of phase current test section 7 output intermittently but substantially can be considered sinusoidal wave, and can be with the characteristic value of this waveform (for example, cycle, amplitude, phase place etc.) be considered as basic consistent with the waveform characteristic value of the input signal Ur that inputs to modulation portion 5, therefore according to the waveform characteristic value of input signal Ur, the instant value of the phase current of current switch periods and the phase information of this instant value, can calculate the maximum of this phase current waveform of particular phases in the cycle, the above-mentioned particular phases cycle refers to that the instant value of this phase current is residing phase cycling in the phase current waveform of this phase.The comparing section 83 of over-current judging section 8 compares maximum and the predefined overcurrent fiducial value of above-mentioned phase current waveform, judges whether method generation overcurrent.
Therefore, so long as those skilled in the art are clear, various distortion and the imitation carried out in the scope of the category that does not break away from technological thought of the present invention all belong in protection scope of the present invention.
Claims (13)
1. a frequency-converter device converts industrial power the alternating voltage of optional frequency to and puts on load by the pulse width modulation that utilizes the pwm signal pattern, and this pwm signal pattern is based on carrier signal and input signal generates, it is characterized in that,
Have:
Frequency conversion section, each brachium pontis of this frequency conversion section is connected with each phase line of above-mentioned load respectively, with regard to the arbitrary brachium pontis in above-mentioned each brachium pontis, the connected node that this brachium pontis is connected by the phase line of this brachium pontis and above-mentioned load is divided into top brachium pontis and bottom brachium pontis, be respectively equipped with for the switch element that comes this brachium pontis of on/off according to the said PWM signal pattern at above-mentioned top brachium pontis and bottom brachium pontis
The phase current test section, comprise a plurality of arm resistances and current detecting part, above-mentioned a plurality of arm resistance is separately positioned on the bottom brachium pontis of each brachium pontis of above-mentioned frequency conversion section, and above-mentioned current detecting part is for detection of the voltage at the two ends of above-mentioned each arm resistance and export the phase current of each phase
Over-current judging section, comprise prospective current operational part and comparing section, the phase current of the current switch periods that above-mentioned prospective current operational part will be in based on the switch motion of said PWM signal pattern receives from above-mentioned phase current test section is as benchmark, prediction and calculation after switch periods in the prospective current value that may occur, above-mentioned comparing section compares prospective current value and the predefined overcurrent fiducial value that calculates;
Be above-mentioned overcurrent fiducial value when above in above-mentioned prospective current value, make the circuit overcurrent protection action.
2. frequency-converter device according to claim 1 is characterized in that,
The maximum current upstroke slope that the utilization of above-mentioned prospective current operational part predetermines, according to the phase current values of current switch periods, prior forecast calculates the phase current values of next switch periods adjacent with current switch periods as above-mentioned prospective current value.
3. frequency-converter device according to claim 2 is characterized in that,
Above-mentioned load is alternating current motor,
Be made as Vs at the voltage that will put on above-mentioned motor, the inductance value of above-mentioned motor be made as Ls, when above-mentioned maximum current upstroke slope is made as slope, satisfy following relational expression:
slope=Vs/Ls。
4. frequency-converter device according to claim 3 is characterized in that,
The inductance value of above-mentioned motor is to utilize the automatic regulating function of above-mentioned frequency-converter device to come automatic acquisition.
5. frequency-converter device according to claim 3 is characterized in that,
Be made as iu1 at the phase current with above-mentioned current switch periods, the phase current of above-mentioned next switch periods be made as iu2, when cycle of above-mentioned carrier signal is made as Ts, satisfy following relational expression:
iu2=slope×Ts+iu1。
6. frequency-converter device according to claim 2 is characterized in that,
Determine that above-mentioned maximum current upstroke slope adopts following method: the upstroke slope of the output current of actual measurement frequency-converter device and make up database in the real-world operation process, and continue the maximum upstroke slope in the upstroke slope of these output currents is upgraded, determine thus above-mentioned maximum current upstroke slope.
7. frequency-converter device according to claim 6 is characterized in that,
Be made as iu1 at the phase current with above-mentioned current switch periods, the phase current of above-mentioned next switch periods be made as iu2, cycle of above-mentioned carrier signal is made as Ts, when above-mentioned maximum current upstroke slope is made as slope, satisfy following relational expression:
iu2=slope×Ts+iu1。
8. each described frequency-converter device in 7 according to claim 1 is characterized in that, 2～3 times of the rated current that above-mentioned overcurrent fiducial value is above-mentioned frequency-converter device.
9. each described frequency-converter device in 7 according to claim 1 is characterized in that,
Above-mentioned current detecting part comprises:
Current detector, the voltage at the two ends of above-mentioned each arm resistance of detection, Flow is crossed the electric current of above-mentioned each arm resistance thus;
The phase current operational part according to the current value that above-mentioned current detector calculates, calculates and exports the phase current of each phase.
10. frequency-converter device according to claim 9 is characterized in that, above-mentioned current detector is integrated operational amplifier.
11. frequency-converter device according to claim 10 is characterized in that, above-mentioned arm resistance is noninductive resistance.
12. frequency-converter device according to claim 1, it is characterized in that, according to the phase current values of the waveform characteristic value of above-mentioned input signal, above-mentioned current switch periods and the phase information of this phase current values, calculate the maximum of waveform of this phase current of particular phases in the cycle as above-mentioned prospective current value, the above-mentioned particular phases cycle refers to that this phase current values is residing phase cycling in the phase current waveform of this phase.
13. the overcurrent protection method of a frequency-converter device; by the pulse width modulation that utilizes the pwm signal pattern industrial power is converted to the alternating voltage with optional frequency and puts on load; this pwm signal pattern is based on carrier signal and input signal generates, and it is characterized in that
Above-mentioned frequency-converter device has:
Frequency conversion section, each brachium pontis of this frequency conversion section is connected with each phase line of above-mentioned load respectively, with regard to the arbitrary brachium pontis in above-mentioned each brachium pontis, the connected node that this brachium pontis is connected by the phase line of this brachium pontis and above-mentioned load is divided into top brachium pontis and bottom brachium pontis, be respectively equipped with for the switch element that comes this brachium pontis of on/off according to the said PWM signal pattern at above-mentioned top brachium pontis and bottom brachium pontis
A plurality of arm resistances are separately positioned on the bottom brachium pontis of each brachium pontis of above-mentioned frequency conversion section;
The overcurrent protection method of above-mentioned frequency-converter device comprises:
Determine the step of maximum current upstroke slope,
Detect the voltage at the two ends of above-mentioned each arm resistance, and calculate the phase current of each phase of current switch periods and the step of carrying out the A/D conversion according to detected voltage,
On the basis of the phase current values of the current switch periods that A/D changed and above-mentioned maximum current upstroke slope, the step of the expection phase current values of next switch periods that prediction and calculation is adjacent with current switch periods,
With the expection phase current values of next switch periods of calculating and the step that predefined overcurrent fiducial value compares;
Be above-mentioned overcurrent fiducial value when above in above-mentioned prospective current value, make the circuit overcurrent protection action.
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Address after: LS Le Xing Lu Industrial Park National hi tech Industrial Development Zone of Wuxi City, Jiangsu province 214028 Patentee after: Lexing electric (Wuxi) Co.,Ltd. Address before: LS Le Xing Lu Industrial Park National hi tech Industrial Development Zone of Wuxi City, Jiangsu province 214028 Patentee before: LS INDUSTRIAL SYSTEMS Co.,Ltd. |